This invention relates to improvements in the ammunition art, and specifically to improvements in the ammunition of the type used in high power rifles of all calibers in which an elastomer or plastic is used for a predominant portion of the casing which houses the powder and positions the projectile. The casing is made of a synthetic polymer composition attached to a metallic head positioned at the opposite end of the cartridge from the projectile.
Cartridges of this general type have been known in the literature for many years but have for one reason or another, failed to provide a satisfactory ammunition for sustained automatic fire in the modern automatic weapons widely used in police, paramilitary and military situations.
The following patents are known to disclose various types of composite cartridges of the general type to which this invention is addressed:
______________________________________ INVENTOR ______________________________________ U.S. Pat. Nos. 2,654,319 Roske 2,862,446 Ringdal 3,026,802 Barnet et al. 3,099,958 Daubenspeck, et al. 3,745,924 Scanlon 3,842,739 Scanlon, et al. 3,874,294 Hale 3,977,326 Anderson 4,147,107 Ringdal UNITED KINGDOM 1,015,516 Daubenspeck et al. GB2,044,416 Application Hebert EUROPEAN PATENT APPLICATION 0 131 863 (Publn. 23.01.85) Vatsvog GERMAN PATENT 2,419,881 ______________________________________
Cartridges of this type are also used in large quantities as blank rifle cartridges in which the head end of the cartridge case continues into the imitation shape of a plastic projectile which constitutes an integral part of the cartridge case and has a notch or groove forming a predetermined rupture zone. These cartridges are loaded with a nominal amount of powder and are used as training and simulation aids without a projectile of the usual type. Because of the nominal loading of powder, cartridges of this type may not develop enough chamber pressure to operate the gas-operated automatic ejection and reloading mechanisms used in military type automatic weapons.
It is recognized that a plastic rifle cartridge should usually have a metal cap or head to carry the primer and to provide the ejection groove necessary to eject the spent cartridge from the firing chamber. When used in a modern automatic weapon the need is also present for a reinforced cap or head area to contain residual pressures in the cartridge occasionally encountered when the ejection cycle begins removal of the cartridge from the chamber before the pressure effects of the recent firing have fully dissipated. To achieve consistent performance, both ballistically and in the operation of the gas operated ejection mechanism, a rifle cartridge must develop a consistently high chamber pressure level for each round. Heretofore, the attainment of consistent pressure levels has been difficult, due to inconsistencies in the interfit between the bullet and the cartridge, improper sizing of the powder chamber for the powder used, and to the many variations in the performance in the burning cycle of the various powders available for use in rifle ammunition.
Conventional cartridges for rifles and machine guns, as well as larger caliber weapons are usually made with brass casings. The brass casing includes an integrally formed head containing a primer cup to receive a primer adapted to ignite a powder charge at one end, and at the other end provides a mechanical interfit to a bullet. The grip of the cartridge upon the bullet, together with the amount and characteristics of the powder, the interior volume of the powder chamber and other factors determine the chamber pressure levels developed during the firing cycle. The bullet or other projectile is held in place with a crimp or frictional engagement, the strength of which is a factor in determining the pressure needed to initiate bullet movement into the barrel of the rifle. Brass casings can be reloaded and thereby reused but suffer from several disadvantages, including weight. In addition, special tooling is necessary for reloading. Brass is also a relatively expensive metal which may be in short supply in some areas of the world, particularly in the event of war.
Expendable aluminum casings have been developed but generally are not reusable, making the ultimate cost of the aluminum casing comparable to brass. An extensive amount of precision metalworking equipment is necessary to form the casings from either brass or aluminum.
Several attempts have been made to develop a reusable handgun casing made of lightweight plastic materials, including my successful development described in my European Patent Application No. 0 131 863. In the use of plastic casings of the prior art, it is necessary that there be a tight fit between the casing and the bullet and between the casing and the head in order to prevent the escape of the gases formed when the powder charge is ignited. These gases in the handgun loads can quickly reach a pressure of over 10,000 psi, and thus the seal around the bullet and around the head must be tight enough to prevent the escape of the gases until the bullet is discharged. In rifle applications, such as the NATO 5.56 mm (.223 caliber) widely used in weapons such as the M-14 and M-15 used by the United States of America and its allies and various 5.56 mm rifles used by Warsaw pact forces pressures of 40,000 to 60,000 psi or higher may be encountered. The seal around the head is of extreme importance at these higher pressures as well as the strength of the head extending along a substantial distance of the side wall of the cartridge to prevent rupture of the sidewall of the cartridge during ejection of the spent cartridge. Such a rupture and escape of the gases would not only adversely effect the performance of the bullet being discharged but would also potentially adversely affect the subsequent firing of the rifle and could present a safety hazard to the rifleman or his companions.
Of great significance is the need to controllably maintain the chamber pressure developed by detonation or burning of the powder during the firing cycle so that a consistent pressure level is attained for a given powder load and type. In brass cased ammunition the pressure level is attained during and following burning of the powder in part through the crimp or frictional interfit between the bullet and the inner wall of the case. With plastic cases the control of the pressures has heretofore been erratic and unacceptable.
For military rounds, the need for reloading capability is minimized, so long as the round is relatively inexpensive to manufacture and load, and so long as the other desirable factors of the cartridge, such as corrosion resistance, weight, moisture resistance and the like provide a cartridge as dependable as brass.
Brass cartridges rely upon the crimp or frictional engagement with the bullet to control the buildup of pressure before bullet ejection. A more consistent and reliable control would provide more nearly consistent ballistics performance and is one of the attributes of this invention.
In all of the patents mentioned above the cartridge is formed of a composite plastic or metal and plastic casings which rely on multiple parts to provide the sealing around the end caps or head, and require a crimp about the bullet to hold the bullet in place. The cost of producing and assembling a multiple piece casing is high and heretofore the composite casings have not accomplished the dual functions of sealing the head to the plastic casing and the plastic casing to the bullet in a manner which permits the resulting cartridge to be used in fully automatic rifle firing applications.